Multiphoton analysis of the free electron laser

A model of the free electron laser is proposed which is based on the classical current of the electron in the wiggler field interacting with a quantized radiation field. To calculate the gain, the quantum recoil for the processes of n-photon emission and absorption must be put in by hand from kinematical considerations. Apart from a spontaneous emission term the gain agrees essentially with the usual small signal expression, for the radiation field being in either an eigenstate of photon number or in a coherent state. The distribution of the electrons after the interaction is, however, essentially quantum mechanical.     

Two-Slit and Aharonov-Bohm Experiments in Magnetic Field

We discuss the two-slit experiment and the Aharonov-Bohm (AB) experiment in the magnetic field. In such a case the electron moving in the magnetic field produces so called synchrotron radiation. In other words the photons are emitted from the points of the electron trajectory and it means that the trajectory of electron is visible in the synchrotron radiation spectrum. The axiomatic system of quantum mechanics does not enable to define the trajectory of the elementary particle. The two-slit experiment and AB experiment in a magnetic field was never performed and it means that they are the missing experiments of quantum mechanics. The extension of the discussion to the cosmical rays moving in the magnetic field of the Saturn magnetosphere and its rings is mentioned. It is related to the probe CASSINI. The solution of the problem in the framework of the hydrodynamical model of quantum mechanics and the nonlinear quantum mechanics is also mentioned.     

Impurity-related optical response in a 2D and 3D quantum dot with Gaussian confinement under intense laser field

ABSTRACT

Using the two-dimensional (2D) diagonalisation method, the impurity-related electronic states and optical response in a 2D quantum dot with Gaussian confinement potential under nonresonant intense laser field are investigated. The effects of a hydrogenic impurity on the energy spectrum and binding energy of the electron and also intersubband optical absorption are calculated. The obtained numerical results show that the degeneracies of the excited electron states are broken and the absorption spectrum exhibits a redshift with the values of the laser field. The findings indicate a new degree of freedom to tune the performance of novel optoelectronic devices, based on the quantum dots and to control their specific properties by means of intense laser field and hydrogenic donor impurity. Using the same Gaussian confinement model, the electronic properties of a confined electron in the region of a spherical quantum dot are studied under the combined effects of on-centre donor impurity and a linearly polarised intense laser radiation. The three-dimensional problem is used to theoretically model, with very good agreement, some experimental findings reported in the literature related to the photoluminescence peak energy transition.     

Quantum radiation reaction effects in multiphoton Compton scattering

Radiation reaction effects in the interaction of an electron and a strong laser field are investigated in the realm of quantum electrodynamics. We identify the quantum radiation reaction with the multiple photon recoils experienced by the laser-driven electron due to consecutive incoherent photon emissions. After determining a quantum radiation dominated regime, we demonstrate how in this regime quantum signatures of the radiation reaction strongly affect multiphoton Compton scattering spectra and that they could be measurable in principle with presently available laser technology.     

Oscillations of the magnetoresistance of a two-dimensional electron gas in a GaAs quantum well with AlAs/GaAs superlattice barriers in a microwave field

The effect of microwave radiation in the frequency range from 1.2 to 10 GHz on the magnetoresistance of a high-mobility two-dimensional electron gas has been studied in a GaAs quantum well with AlAs/GaAs superlattice barriers. It has been found that the microwave field induces oscillations of this magnetoresistance, which are periodic in the reciprocal magnetic field (1/B). It has been shown that the period of these oscillations in the frequency range under study depends on the microwave radiation power.     

Once upon a time,in the Soviet Union …

Radiation reaction (but, more generally, fluctuations and dissipation) occurs when a system interacts with a heat bath, a particular case being the interaction of an electron with the radiation field. We have developed a general theory for the case of a quantum particle in a general potential (but, in more detail, an oscillator potential) coupled to an arbitrary heat bath at arbitrary temperature, and in an external time-dependent c-number field. The results may be applied to a large variety of problems in physics but we concentrate by showing in detail the application to the blackbody radiation heat bath, giving an exact result for the radiation reaction problem which has no unsatisfactory features such as the runaway solutions associated with the Abraham–Lorentz theory. In addition, we show how atomic energy and free energy shifts due to temperature may be calculated. Finally, we give a brief review of applications to Josephson junctions, quantum statistical mechanics, mesoscopic physics, quantum information, noise in gravitational wave detectors, Unruh radiation and the violation of the quantum regression theorem.     

Spectrum of indirect magnetoexcitons in coupled quantum wells

The indirect Mott exciton (spatially-separated electron and hole) in coupled quantum wells in crossed electric and magnetic fields is discussed. The exciton spectrum is calculated for the case where the distance between the quantum wells of the electron and hole is larger than the exciton Bohr radius. The magnetoexciton creation probability is calculated and its dependence on the electric field is found. The absorption of electromagnetic radiation between the indirect magnetoexciton levels in coupled quantum wells is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 2220–2223 (December 1997)     

Evolution of the theory of a “luminous” electron

A brief survey is presented here of studies contributing to the theory of synchrotron radiation and several quantum effects which accompany the motion of electrons in a magnetic field. Equations which describe the amplitude characteristics of radial and axial oscillations of an electron moving in a nonuniform magnetic field with a weak focus are derived on the basis of the quantum theory. The characteristics of electron spin are analyzed, with oscillations in a nonuniform field (spontaneous polarization) taken into account. Depolarizing spin resonances in accumulators are interpreted in terms of the quantum theory.     

Largest Terrestrial Electromagnetic Pulsar

The power spectrum formula of the synchrotron radiation generated by the electron and positron moving at the opposite angular velocities in homogenous magnetic field is derived in the Schwinger version of quantum field theory. It is surprising that the spectrum depends periodically on radiation frequency which means that the system composed from electron, positron, and magnetic field forms the pulsar.     

Magnetoresistance oscillations due to Zener tunneling and microwave radiation in a 2D electron gas in GaAs quantum well with AlAs/GaAs superlattices barriers

The effect of microwave radiation in the frequency range from 1.2 to 10 GHz on the magnetoresistance of a high-mobility two-dimensional electron gas has been studied in a GaAs quantum well with AlAs/GaAs superlattice barriers. It has been found that the microwave field induces magnetoresistance oscillations periodic in the reciprocal magnetic field (1/B). It has been shown that the period of these oscillations in the covered frequency range depends on the microwave radiation power.     

Thomson and Compton scattering with an intense laser pulse

Our paper concerns the scattering of intense laser radiation on free electrons and it is focused on the relation between nonlinear Compton and nonlinear Thomson scattering. The analysis is performed for a laser field modeled by an ideal pulse with a finite duration, a fixed direction of propagation and indefinitely extended in the plane perpendicular to it. We derive the classical limit of the quantum spectral and angular distribution of the emitted radiation, for an arbitrary polarization of the laser pulse. We also rederive our result directly, in the framework of classical electrodynamics, obtaining, at the same time, the distribution for the emitted radiation with a well defined polarization. The results reduce to those established by Krafft et al. [Phys. Rev. E 72, 056502 (2005)] in the particular case of linear polarization of the pulse, orthogonal to the initial electron momentum. Conditions in which the differences between classical and quantum results are visible are discussed and illustrated by graphs.     

Quantum phenomena and the zeropoint radiation field

The stationary solutions for a bound electron immersed in the random zeropoint radiation field of stochastic electrodynamics are studied, under the assumption that the characteristic Fourier frequencies of these solutions are not random. Under this assumption, the response of the particle to the field is linear and does not mix frequencies, irrespectively of the form of the binding force; the fluctuations of the random field fix the scale of the response. The effective radiation field that supports the stationary states of motion is no longer the free vacuum field, but a modified form of it with new statistical properties. The theory is expressed naturally in terms of matrices (or operators), and it leads to the Heisenberg equations and the Hilbert space formalism of quantum mechanics in the radiationless approximation. The connection with the poissonian formulation of stochastic electrodynamics is also established. At the end we briefly discuss a few important aspects of quantum mechanics which the present theory helps to clarify.On leave of absence at Mathematics Department, University College London. Gower Street, London WC1, U.K.     

Optical exciton Stark effect and quantum beats at exciton quasienergy levels in quantum wells

The optical Stark effect and quantum beats in a GaAs/AlGaAs quantum well are investigated theoretically for the case when the first two electron size-quantization levels are mixed dynamically by a high-intensity CO₂ laser pulse polarized perpendicular to the plane of the quantum well. The quasienergy spectrum of heavy-hole excitons and the ratio between the probabilities of exciton transition with and without a strong electromagnetic field are obtained. The time-dependent intensity of absorption of the sensing light is determined. It exhibits quantum beats at twice the electron Rabi frequency. Fiz. Tverd. Tela (St. Petersburg) 39, 1291–1294 (July 1997)     

Giant magnetoresistance oscillations induced by microwave radiation and a zero-resistance state in a 2D electron system with a moderate mobility

The effect of a microwave field in the frequency range from 54 to 140 GHz on the magnetotransport in a GaAs quantum well with AlAs/GaAs superlattice barriers and with an electron mobility no higher than 10⁶ cm²/V s is investigated. In the given two-dimensional system under the effect of microwave radiation, giant resistance oscillations are observed with their positions in the magnetic field being determined by the ratio of the radiation frequency to the cyclotron frequency. Earlier, such oscillations had only been observed in GaAs/AlGaAs heterostructures with much higher mobilities. When the samples under study are irradiated with a 140-GHz microwave field, the resistance corresponding to the main oscillation minimum, which occurs near the cyclotron resonance, appears to be close to zero. The results of the study suggest that a mobility value lower than 10⁶ cm²/V s does not prevent the formation of zero-resistance states in a magnetic field in a two-dimensional system under the effect of microwave radiation.     

A Model Detector for Hawking Radiation from a Schwarzschild Black Hole

A model detector for field quanta is considered from the point of view of a quantum field theory defined in asymptotically stationary regions of the Kruskal manifold and from that of a theory restricted to a Schwarzschild coordinate patch. A spherical array of oscillators at a constant distance r from the black hole, harmonic with respect to their proper time, is coupled to spherically symmetric Schwarzschild-modes of the field. The system is quantized and the energy expectation value of the coupled harmonic oscillators in a state of the field representing Hawking radiation is calculated. The back-reaction to the field may be interpreted in two controversial ways: In terms of the quantum field theory restricted to Schwarzschild space-time there is merely some scattering of the Hawking radiation, whereas in the framework of Kruskal quantum field theory particle production occurs.     

Field emission graphene–oxide–silicon field effect based photodetector

Silicon‐based devices keep moving into smaller dimension for improving the speed, efficiency, and low‐power consumption. Novel designed semiconductor device architectures are needed to overcome the physical limitations. An integration of well‐designed nanostructure and nanomaterials can potentially establish new principles and approaches to nanoelectronic and photonic devices. We herein demonstrate a graphene/SiO₂/p‐Si (GOS) heterostructure with an embedded nanoscale mesa, forming a GOS‐Mesa field‐effect photodetector. The proposed structure exhibits that multiple exciton generation (MEG) can occur in a quantum‐confined two‐dimensional electron gas (2DEG) region via impact ionization, leading to high internal quantum efficiency (η_IQE). The numerical simulation of the carrier multiplication (CM) factor in our designed structure finds a reasonable agreement with empirical data. Simulated and measured internal quantum efficiency demonstrate ～195% and ～135% of UV–Vis radiation, respectively. A vertically confined 2DEG plays an important role not only in enabling the electron emission process which is responsible for the flowing of electron current, but also in developing a highly localized electric field (up to ～10⁶ V/cm) at the SiO₂/Si interface, enabling an impact ionization process under photon energy of merely ～1.95 eV. Our findings demonstrate that carrier multiplication can be achieved in a suitably designed nanoscale structure in conjunction with nanomaterial on silicon‐based devices, providing incentive to better understand MEG within quantum wells in 2DEG systems, and being a research path to enhancing the efficiency of future solar harvesting technologies. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Quantum regime of a plasma‐wave‐pumped free‐electron laser in the presence of an axial magnetic field

The quantum regime of a plasma‐whistler‐wave‐pumped free‐electron laser (FEL) in the presence of an axial‐guide magnetic field is presented. By quantizing both the plasma whistler field and axial magnetic field, an N‐particle three‐dimensional Hamiltonian of quantum‐FEL (QFEL) has been derived. Employing Heisenberg evolution equations and introducing a new collective operator which controls the vertical motion of electrons, a quantum dispersion relation of the plasma whistler wiggler has been obtained analytically. Numerical results indicate that, by increasing the intrinsic quantum momentum spread and/or increasing the axial magnetic field strength, the bunching and the radiation fields grow exponentially. In addition, a spiking behavior of the spectrum was observed with increasing cyclotron frequency which provides an enormous improvement in the coherence of QFEL radiation even in a limit close‐to‐classical regime, where an overlapping of these spikes is observed. Also, an upper limit of the intrinsic quantum momentum spread which depends on the value of the cyclotron frequency was found.     

High-Field Phenomena of Qubits

Electron and nuclear spins are very promising candidates to serve as quantum bits (qubits) for proposed quantum computers, as the spin degrees of freedom are relatively isolated from their surroundings and can be coherently manipulated, e.g., through pulsed electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR). For solid-state spin systems, impurities in crystals based on carbon and silicon in various forms have been suggested as qubits, and very long relaxation rates have been observed in such systems. We have investigated a variety of these systems at high magnetic fields in our multifrequency pulsed EPR/ENDOR (electron nuclear double resonance) spectrometer. A high magnetic field leads to large electron spin polarizations at helium temperatures, giving rise to various phenomena that are of interest with respect to quantum computing. For example, it allows the initialization of both the electron spin as well as hyperfine-coupled nuclear spins in a well-defined state by combining millimeter and radio-frequency radiation. It can increase the T ₂ relaxation times by eliminating decoherence due to dipolar interaction and lead to new mechanisms for the coherent electrical readout of electron spins. We will show some examples of these and other effects in Si:P, SiC:N and nitrogen-related centers in diamond.     

Dissociative recombination of electrons and O 2 + molecular ions in the field of intense visible laser radiation

We analyze the low-temperature dissociative recombination reaction e ^?+O ₂ ⁺ → O(¹ D)+O(³ P) in the field of visible monochromatic laser radiation. The analysis is performed in terms of the multichannel quantum defect theory using the stationary formalism of the radiative collision matrix. We calculate the dependences of the reaction cross section on the incident electron energy, the external electromagnetic field strength and frequency, and also the angle between the directions of the electron beam and the electric vector for linearly polarized radiation. The cross section is shown to increase by several orders of magnitude for a certain choice of these parameters, suggesting the possible laser stimulation of this reaction.